Patent Application
20100236794
1. Field of Invention
The invention is directed to sealing devices used in oil and gas wellbores to seal the wellbore and, in particular, to sealing devices having shape memory materials that remain in a compressed state until wellbore fluid, such as oil or water, contacts the shape memory material so that the shape memory material can expand and seal the wellbore.
2. Description of Art
Packers having swellable materials encased within an expandable sealing element such as a rubber casing or balloon are known in the art. These types of packers expand and, thus, seal to the inner wall surface of a wellbore by contacting hydraulic fluid or other fluid with the swellable materials encased within the rubber casing so that the swellable materials absorb the fluid and expand. In one type of these packers, for example, hydraulic fluid is pumped down a string of tubing having the packer secured thereto. The hydraulic fluid travels down the bore of the string of tubing and through a port that is in fluid communication with an inner cavity of the rubber casing. Swellable materials disposed within the rubber casing are contacted by the hydraulic fluid. As a result, the swellable materials absorb the fluid and expand. As the swellable materials expand and hydraulic fluid is pumped into the rubber casing, the rubber casing expands to seal the wellbore. After expansion, hydraulic fluid pressure is decreased and the rubber casing remains is held in the expanded position solely by the swellable materials having absorbed the fluid. The swellable materials, however, become softer and lack desirable prolonged strength after expansion because the fluid, which is considered a solvent, reduces intramolecular van der Waals interactions. As a result, packers relying on swellable materials to create a seal with an inner wall surface of the wellbore can prematurely fail because the swellable materials become weaker.
Broadly, downhole tools and, in particular, sealing elements or devices such as packers, are disclosed. The sealing devices include one or more shape-memory materials that are run-in to the wellbore in a compressed shape or position. The shape-memory material is held in the compressed shape by an adhesion material. The adhesion material is dissolvable by a fluid placed in contact with the adhesion material such that when the adhesion material comes into contact with the fluid, the adhesion material dissolves. In certain embodiments, the adhesion material is dissolvable by water. In other embodiments, the adhesion material is dissolvable by a hydrocarbon such as oil.
After the sealing device having the shape-memory material is located at the desired location within the well, the shape-memory material is contacted with the fluid that dissolves the adhesion material. After dissolution of the adhesion material, the shape-memory material is allowed to expand to its pre-compressed shaped, i.e., its original, expanded shape or set position. The expanded shape or set position, therefore, is the shape of the shape-memory material after it is manufactured and before it is compressed. In other words, the shape-memory material possesses hibernated shape memory that provides a shape to which the shape-memory material naturally takes after its manufacturing.
As a result of the shape-memory material being expanded to its set position, the shape-memory material seals the annulus of the wellbore. Although the shape-memory material expands due to its contact with the dissolving fluid, it is to be understood that the shape-memory material returns to its original, expanded shape due to the shape-memory characteristics of the shape-memory material and not due to the shape-memory material absorbing any fluid. In other words, even though fluid may enter into pores, cells, or crevices of the shape-memory material, the fluid so disposed is not required to maintain the shape-memory material in the original, expanded shape.
In one specific embodiment, the shape-memory materials is a polyurethane foam material that is extremely tough and resilient and that is capable of being compressed and returned to substantially its original expanded shape. The polyurethane foam material is held in the compressed state by an adhesion material. Once the adhesion material is dissolved, the polyurethane foam material is no longer held in its compressed or run-in shape and, thus, the polyurethane foam material expands toward its original shape. In so doing, the polyurethane foam material engages the inner wall surface of the wellbore, either directly or indirectly such as by having a rubber outer shell covering the polyurethane foam material. In certain embodiments, the inner wall surface of the wellbore is defined by the inner diameter of wellbore casing. In other embodiments, the inner wall surface of the wellbore is “open-hole,” i.e., defined by the hole drilled into the earth formation.
While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
Referring now to
Water is included as part of the polyol portion and acts as a blowing agent to provide a foam structure because of carbon dioxide generated from the reaction between isocyanate and water when the isocyanate portion and the polyol portion are combined.
In one embodiment, the isocyanate portion contains modified MDI Mondur PC and the polyol portion contains (1) polyester polyol, which consist of a trimethylolpropane branched diethylene glycol adipate sold under the commercial name as Fomrez 45 from Crompton Corporation; (2) chain extender aromatic diamine Dimethylthiotoluenediamine (“DMTDA”) sold by Albemarle under the commercial name Ethacure 300; (3) catalysts; (4) surfactant; and (5) water. The chain extender is a liquid slower polyurethane curative that provides enhanced high temperature properties. The catalyst and surfactant are added into the polyol portion to control final foam cell structure, either open or close, as well as the foam physical properties. In certain embodiments, either amine or metal-based catalysts are included to achieve good properties of polyurethane foam materials. Such catalysts are commercially available from companies such as Air Products. Suitable catalysts that provide especially good properties of polyurethane foam materials include pentamethyldipropylenetriamine, an amine-based catalyst sold under the commercial name Polycat 77 by Air Products, dibutyltindilaurate, a metal-based catalyst sold under the commercial name DABCO T-12 by Air Products.
A small amount of surfactant, e.g., 0.5% of total weight, such as the surfactant sold under the commercial name DABCO DC-198 by Air Products, can be added to control foam cell structure and distribution. Colorant may be added in the polyol portion to provide desired color in the finished product. Such colorants are commercially available from companies such as Milliken Chemical which sells a suitable colorant under the commercial name Reactint.
After the isocyanate portion and the polyol portions are prepared, they are combined together at a desired temperature. The temperature at which the two portions are combined determines the degree of cell size within the resultant polyurethane foam material. For example, higher temperatures of the mixture provide larger cell size while lower temperatures of the mixture provide smaller cell size.
In one particular embodiment, the polyester polyol comprising of a trimethylolpropane branched diethylene glycol adipate sold under the commercial name as Fomrez 45 from Crompton Corporation, is pre-heated to 100° C. before combining with the isocyanate portion. The isocyanate portion is the combined with the polyol portion and a foaming reaction is immediately initiated and the mixture's viscosity increases rapidly.
In another particular embodiment, the polyol comprising of poly(1,6-hexanediol carbonate) polyol sold by Arch Chemicals under the commercial name Poly-CD220 is preheated to 100° C. before combing with the isocyanate portion. The isocyanate portion is then combined with the polyol portion and a foaming reaction is immediately initiated and the mixture's viscosity increases rapidly. The resulting foam made from polycarbonate polyols has a high resistance to hydrolysis and oil attacks.
Due to the high viscosity of the mixture and the reaction occurring quickly, a suitable mixer is recommended to form the polyurethane foam material. Although there are many commercially available fully automatic mixers specially designed for two-part polyurethane foam processing, it is found that mixers such as KitchenAid type mixers with single or double blades work particularly well. In large-scale mixing, eggbeater mixers and drill presses work particularly well.
In mixing the isocyanate and polyol portions, the amount of isocyanate and polyol included in the mixture should be chemically balanced according to their equivalent weight. In one specific embodiment, 5% more isocyanate by equivalent weight is combined with the polyol portion.
In one embodiment, the polyol portion is formed by 50 g of Fomrez 45 polyester polyol is combined with 1.6 g of water, 1.5 g of DMTDA chain extender, 0.1 g of Polycat 77 catalyst, 0.5 g of DABCO DC-198 surfactant, and 0.5 g of Reactint colorant to form the polyol portion. The polyol portion is preheated to 100° C. and mixed in a KitchenAid type single blade mixer with 40.4 of MDI Mondur PC. As will be recognized by persons of ordinary skill in the art, these formulations can be scaled-up to form larger volumes of this shape-memory material.
In another embodiment, the polyol portion is formed by 50 g of Poly-CD220 polycarbonate polyol is combined with 1.6 g of water, 1.5 g DMTDA chain extender, 0.1 g of Polycat 77 catalyst, 0.5 g DABCO DC-198 surfactant, and 0.5 g Reactint colorant to form the polyol portion. The polyol portion is preheated to 100° C. and mixed in a KitchenAid type single blade mixer with 41.5 g of MDI Mondur PC. As will be recognized by persons of ordinary skill in the art, these formulations can be scaled-up to form larger volumes of this shape-memory material.
The mixture containing the isocyanate portion and the polyol portion is mixed for about 20 seconds and then poured into a mold and immediately closed by placing a top metal plate on the mold. Due to the significant amount of pressure generated by the foam-forming process, a C-clamp can be used to hold the top metal plate and mold together to prevent leakage of the mixture from the mold. After approximately 2 hours, the polyurethane foam material is sufficiently cured such that the mold can be removed. Thereafter, in one specific embodiment, the polyurethane foam material is treated “post-cure” at a temperature of 100° C. for approximately 6 hours so that the polyurethane foam material reaches its full strength.
Additionally, the polyurethane foam material at this stage will, almost always, include a layer of “skin” on the outside surface of the polyurethane foam. The “skin” is a layer of solid polyurethane elastomer formed when the mixture contacts with the mold surface. It is found that the thickness of the skin depends on the concentration of water added to the mixture. Excess water content decreases the thickness of the skin and insufficient water content increases the thickness of the skin. The formation of the skin is believed to be due to the reaction between the isocyanate in the mixture and the moisture on the mold surface. Therefore, additional mechanic conversion processes are needed to remove the skin. Tools such as band saws, miter saws, or hack saws may be used to remove skin. After removing the skin from the polyurethane foam material, it will have a full open cell structure, excellent elasticity, and very good tear strength.
At this point, the polyurethane foam material is in its original, expanded, shape having an original, or expanded, thickness 36 (
Prior to including the polyurethane foam material as part of sealing device 30, the polyurethane foam material is saturated in an adhesion material. Suitable adhesion materials include water and isopropyl alcohol dissolvable polymers such as poly(vinyl pyrrolidone) sold by International Specialty Products under the commercial name PVP K-30. This adhesion material is used for water-triggered shape-memory polyurethane foam materials. Any polymers that are dissolvable in oil and solvent can be used for as adhesion materials for oil-triggered shape-memory materials. Suitable polymers for these applications include polystyrene, poly)methyl methacrylate), etc.
The adhesion materials are usually supplied in the form of solid powders or pellets. Therefore, the adhesion material solution has to be prepared before use. For one specific example of water-triggered adhesion material solution, 30% PVP K-30 and 70% isopropyl alcohol (“IPA”) by weight are mixed together. For one specific example of an oil-triggered adhesion material solution, 30% polystyrene pellets and 70% Methyl Isobutyl Ketone (“MIBK”) by weight are mixed together.
After saturation of the polyurethane foam material in the adhesion material solution, a vacuum at approximately 762 mm Hg is applied to the polyurethane foam material so that the adhesion material solution can penetrate throughout the cells of the polyurethane foam material, air trapped inside the polyurethane foam material can be removed, and voids within the polyurethane foam material can be replaced with the adhesion material solution.
The polyurethane foam material impregnated with the adhesion material solution is then placed between two metal plates and mechanically compressed from its original, or expanded, thickness of about 20 mm to approximately 14 mm or less. In one specific embodiment, the polyurethane foam material impregnated with the adhesion material solution is compressed from an original thickness to about 50% of the original thickness. In another embodiment, the polyurethane foam material impregnated with the adhesion material is compressed from an original thickness to about 30% of the original thickness. Spacers and c-clamps can be used to control finished thickness. The compressed polyurethane foam material is then placed inside a vacuum oven and heated to 80° C. for approximately 8 hours or more to remove all of the liquid used to suspend the adhesion material from the polyurethane foam material.
After all of this suspending liquid is removed from the polyurethane foam material, the finished polyurethane foam material is stable in its compressed position or shape at dry conditions and has compressed, or run-in, thickness 34. The polyurethane foam material can then be installed onto a base pipe with a permanent bonding material so that the polyurethane foam material forms sealing device 30. Alternatively, the polyurethane foam material may be included as part of sealing device 30 such as by including a rubber casing over the polyurethane foam material in place of the prior art swellable absorbent materials.
The impregnated polyurethane foam material remains in its compressed state, or run-in position, during run-in of the sealing device 30 into wellbore 50. The impregnated polyurethane foam material also remains in the run-in position until the correct fluid contacts the impregnated polyurethane foam material for a sufficient amount of time so that the adhesion material dissolves and the polyurethane foam material can expand to the set or expanded position. The correct fluid may be water, oil, or some other type of fluid. The correct fluid is determined based upon the adhesion material utilized in forming the impregnated polyurethane foam material. If the adhesion material is dissolvable in water, then the correct fluid is water. If the adhesion material is dissolvable in oil, then the correct fluid is oil.
In the embodiment in which the correct fluid is water, the water dissolves the adhesion material. As a result, the forces holding the impregnated polyurethane foam weaken until the point that the energy stored in the polyurethane foam material are greater than the adhesion forces provided by the adhesion material. At that point, the polyurethane foam material expands from its compressed position to its original shape as formed prior to impregnation and compression. In so doing, the polyurethane foam material contacts inner wall surface 54 of wellbore 50 to establish a seal that divides annulus 60 of the wellbore 50. As will be recognized by persons of ordinary skill in the art, expansion of the polyurethane foam material is not dependent upon absorption of any fluid. Thus, the polyurethane foam material, by itself, provides the expanded shape to establish the seal against inner wall surface 54 of wellbore 50.
Still with reference to
As will be recognized by persons of ordinary skill in the art, sealing device 30 should have an outer diameter around tubing string 42, i.e., original or expanded thickness 36 that is large enough such that expansion of sealing device 30 results in sealing device 30 exerting a force into inner wall surface 54 of wellbore casing 52 so that a sufficient seal can be formed between sealing device 30 and inner wall surface 54 of wellbore casing 52. Therefore, the outer diameter of tubing sting 42, as well as inner diameter of wellbore casing 52 should be taken into consideration when determining the thickness (or outer diameter) formed by sealing device 30. Determining the size of shape-memory material 32 in a given sealing device 30 to provide the desired or necessary sealing between the sealing device and the inner wall surface of the wellbore is easily achieved by persons of ordinary skill in the art in light of the present disclosure.
In one embodiment, the adhesion material is selected based upon its ability to maintain shape-memory material 32 in the compressed position (
The use of shape-memory materials provide prolonged resiliency and strength compared to swellable materials and other materials that rely on absorb fluids to maintain their expanded shapes. Moreover, the shape-memory materials provide their sealing characteristics in their naturally occurring expanded shapes, whereas the swellable materials and other materials that rely on absorbed fluids to maintain their expanded shapes are in their “unnaturally” occurring expanded shape. In other words, the shape-memory materials are energized in their compressed position, and unenergized in their expanded position, whereas the swellable materials are unenergized in their compressed positions and energized in their expanded positions. As a result, the swellable materials have a tendency to release their energy when in their expanded position, thereby weakening the seal against the inner wall surface of the wellbore. On the other hand, the shape-memory materials have no stored energy in their expanded position that, if released, would weaken the seal against the inner wall surface of the wellbore. Thus, any stored energy in the shape-memory materials would only create a greater force into the inner wall surface of the wellbore to increase the strength of the seal against the inner wall surface of the wellbore.
It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11904934 | Sep 2007 | US |
| Child | 12802223 | US |
